The present invention is related to the field of fiber optic devices and networks, and in one embodiment provides a mechanism which varies a wavelength response of one or more fiber Bragg gratings by producing a strain in an optical fiber.
Modern fiber optic communication systems often have the ability to simultaneously transfer light signals having differing wavelengths over a single optical fiber.
Fiber Bragg gratings (FBG) are a particularly advantageous structure for differentiating and manipulating optical signals based on their wavelength. Fiber Bragg gratings are often formed by selectively exposing photosensitive fiber to light, thereby creating a permanent refractive-index grating along the core of the fiber. The resulting sharp reflection resonances can be used as demultiplexers, dispersion compensators, and the like. Fiber Bragg gratings also have applications in communications and sensor areas, operating as resonators, filters, pressure sensing elements, etc. Therefore, fiber Bragg gratings are expected to be important components in many optical communication systems, particularly in the dense wavelength division multiplex systems now being developed.
In operation, a grating is written into a fiber to reflect light of a particular wavelength or band of wavelengths, while other wavelengths of light are transmitted through the grating. Each grating is a wavelength-selective reflector having a reflectance response curve with at least one well-defined peak. If the fiber in which the gratings are written is subjected to a strain, the reflectance peak of the grating shifts. Shifts in the wavelength response may result from changes in environmental temperature, mechanical tension, or vibration.
It has been proposed to make use of the variable wavelength response of fiber Bragg gratings to produce novel optical devices. One proposed tunable fiber bandpass filter is achieved by controlling the strain distribution along the length of a linearly chirped fiber Bragg grating by affixing the grating to each element of a piezoelectric stack. This structure can provide complex filter characteristics such as multiple bandpass peaks, comb filtering, and the like. Unfortunately, this proposed structure will also involve a complex controller, and may result in inconsistent filtering if the coupling between the grating and each piezoelectric element is not tightly controlled. As a result, this phase shift structure appears to be quite difficult to fabricate.
In light of the above, there is a significant need for a fiber optic package that provides a new, yet simple and low cost technique for inducing a phase-shift in a fiber Bragg grating. Therefore, a fiber optic package that subjects a fiber Bragg grating to a controlled strain to produce a desired and predetermined change in a grating wavelength is desired.